This invention relates to optical sensing systems and relates more specifically to so-called optical time domain reflectometry or similar sensing systems in which wavelength referencing techniques are employed whereby light pulses of different wavelengths derived from respective laser sources are launched into optical fiber means and in which the levels of back-scattered light or returned light at different wavelengths arriving back at the launch end of the optical fiber means with respect to time are detected by receiver means which provides an indication of the parameter (eg. temperature or pressure) being measured. The subject matter of the present application is related to the disclosure in copending application Ser. Nos. 131,167 and 131,168, both filed Dec. 10, 1987, and owned in common with the present application.
With optical sensing systems as described above, variations in the relative levels or intensities of the light pulses at different wavelengths produced by the respective laser sources can give rise to inaccuracies in the measurements provided by the receiver means.